Abnormal coronary microvascular vasodilation has been demonstrated in patients with diabetes and metabolic syndrome, but the role of insulin resistance in its pathogenesis is not clear. The aim of this study is to invasively assess coronary microcirculation and to investigate the relationship of insulin resistance with coronary microvascular dysfunction.

A pressure temperature-sensor-tipped coronary wire will be advanced in coronary arteries without significant lumen reduction. Thermodilution-derived coronary flow reserve (CFR) will be calculated as resting mean transit time (Tmn) divided by hyperemic Tmn (obtained with a 5-min i.v. infusion of adenosine 140 mg/kg/min). An index of microvascular resistance (IMR) will be calculated as the distal coronary pressure at maximal hyperemia divided by the inverse of the hyperemic Tmn. FFR will be calculated by the ratio of Pd/Pa at maximal hyperemia. Insulin resistance (IR) will be assess by the homeostasis model assessment (HOMA) index and plasma IL-6 and TNF-alpha levels will be measured in addition to routine blood examinations before the procedure.

Patients will arrive to the cardiac catheterization laboratory in a fasting state without discontinuation of their cardiac medications. After conventional diagnostic coronary angiography, 3000-5000 I.U. i.v. heparin will be administered, and a 6F coronary guiding catheter will be placed in the ostium of the coronary artery of interest. A 0.014" coronary pressure wire (Radi Medical Systems, Wilmington, Mass) will be calibrated, equalized to the guiding catheter pressure with the sensor positioned in the coronary ostium, and then advanced to the distal coronary artery (down to at least two thirds of the epicardial vessel length). Coronary flow reserve (CFR), fractional flow reserve (FFR) and the index of microvascular resistance (IMR) will be measured after an intravenous infusion of adenosine [140 ug/kg/min] to induce steady state maximal hyperemia.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01014949